I <-> 1

roman.py

import argparse
from unittest import TestCase

A = {
  1000: 'M',
  900:  'CM',
  500:  'D',
  400:  'CD',
  100:  'C',
  90:   'XC',
  50:   'L',
  40:   'XL',
  10:   'X',
  9:    'IX',
  5:    'V',
  4:    'IV',
  1:    'I'
}

B = {
  'M':  1000,
  'CM': 900,
  'D':  500,
  'CD': 400,
  'C':  100,
  'XC': 90,
  'L':  50,
  'XL': 40,
  'X':  10,
  'IX': 9,
  'V':  5,
  'IV': 4,
  'I':  1
}

def serialize(v: int) -> str:
  ret = ''
  for key in A:
    rem = v % key
    if v // key > 0:
      ret += (v // key) * A[key]
    v = rem
  return ret

def deserialize(v: str) -> int:
  i = 0; tokens = []
  while i < len(v):
    if i + 1 < len(v):
      t = v[i] + v[i + 1]
      if t in ['CM', 'CD', 'XC', 'XL', 'IX', 'IV']:
        tokens.append(t)
        i += 2
        continue
    tokens.append(v[i])
    i += 1
  return sum(list(map(lambda token: B[token], tokens)))

def cli():
  parser = argparse.ArgumentParser()

  parser.add_argument(
    '--to',
    '-t',
    action = 'store_true',
    help = 'Roman numeral to integer.'
  )

  return parser.parse_args()

def main(args):
  print((lambda v: serialize(int(v)), lambda v: deserialize(v))[args.to](input()))

if __name__ == '__main__':
  try:
    main(cli())
  except Exception as error:
    print(str(error))

class SerializeTestCase(TestCase):
  def setUp(self):
    self.cases = [
      (3,    'III'),
      (58,   'LVIII'),
      (1994, 'MCMXCIV')
    ]

  def test_serialize(self):
    for have, want in self.cases:
      assert serialize(have) == want

class DeserializeTestCase(TestCase):
  def setUp(self):
    self.cases = [
      ('III',     3),
      ('LVIII',   58),
      ('MCMXCIV', 1994)
    ]

  def test_deserialize(self):
    for have, want in self.cases:
      assert deserialize(have) == want